Multiple glazing with variable scattering by liquid crystals and its method of manufacture

ABSTRACT

A multiple glazing with variable scattering by liquid crystals includes first and second flat float glass sheets sealed on the edge of their internal faces by a sealing joint, in particular made of a given sealing material, in particular essentially organic, first and second electrodes, and a layer of liquid crystals with an average thickness E between 15 and 60 μm inclusive of these values and incorporating spacers. The thickness A of each of the first and second glass sheets is less than or equal to 5.5 mm, and each of the internal faces coated with the first and second electrodes has a dioptric defect score, expressed in millidioptres, of less than 12E/15 where the thickness E of the liquid crystals is in μm.

This application is a continuation of U.S. patent application Ser. No.13/820,467, filed Mar. 1, 2013, which is a U.S. National Stage ofPCT/FR2011/051990, filed Aug. 31, 2011, which in turn claims priority toFrench Application No. 1057005, filed Sep. 3, 2010. The content of theseapplications are incorporated herein by reference in their entirety.

The invention relates to the field of electrically controllable glazinghaving variable optical properties, and it more particularly concernsglazing with variable scattering by liquid crystals, provided with alayer of liquid crystals between two glass panes and alternatingreversibly between a transparent state and a non-transparent state byapplication of an alternating electric field.

Glazings are known, certain characteristics of which can be modifiedunder the effect of a suitable electrical supply, more particularly thetransmission, absorption, reflection at certain wavelengths ofelectromagnetic radiation, particularly in the visible and/or infraredranges, or alternatively the scattering of light.

Electrically controllable glazing with liquid crystals can be usedeverywhere, both in the construction sector and in the motor vehiclesector wherever viewing through the glazing needs to be prevented atgiven times.

Document WO 9805998 discloses multiple glazing with liquid crystals,comprising:

-   -   two 1 m² float glass sheets with thicknesses of 6 mm sealed on        the edge of their internal faces by an adhesive sealing joint        made of epoxy resin,    -   two electrodes made of electrically conductive layers based on        SnO₂:F, directly on the internal faces of the glass panes,    -   a 15 μm layer of liquid crystals based on PSCT “Polymer        Stabilized Cholesteric Texture” and incorporating spacers in the        form of 15 μm glass beads directly on the electrodes.

The glass panes are placed in contact by lowering the second glass panewith an inclined angle onto the first glass pane in order to enclose thelayer of liquid crystals, as shown in FIG. 2 and described in greaterdetail below.

Subsequently, after formation of the sealing joint, the glass panes arepressed by passing between two rollers in order to distribute the layerof liquid crystals while evacuating the trapped air, as shown in FIG. 3.

The optical performance and the reliability of this glazing can beimproved. Furthermore, such glazing is expensive, heavy, bulky and inparticular difficult to handle.

It is an object of the invention to develop reliable multiple glazingwith liquid crystals, which has satisfactory optical performance and ispreferably compact.

To this end, the present invention firstly provides multiple glazingwith variable scattering by liquid crystals having:

-   -   first and second flat float glass sheets sealed on the edge of        their internal faces by a sealing joint, in particular made of a        given sealing material, in particular an essentially organic        sealing material,    -   on the internal faces of the first and second glass sheets,        first and second electrodes in the form of transparent        electrically conductive layers provided with a power supply,    -   and, on the first and second electrodes, a layer of liquid        crystals alternating reversibly between a transparent state and        a translucent state by application of an alternating electric        field, which layer has an average thickness E of between 15 and        60 μm inclusive of these values and incorporates spacers, in        particular transparent spacers.

The thickness A of each of the first and second glass sheets is lessthan or equal to 5.5 mm, and each of the internal faces coated with thefirst and second electrodes has a dioptric defect score, expressed inmillidioptres (or mdt), of less than 12 E/15 where the thickness E ofthe liquid crystals is in μm.

The Applicant has discovered the relationship between the quality of theglass panes and the optical performance of the multiple glazing withliquid crystals.

FIG. 1 shows, as reference glazing, an assembly of two standard thinglass panes 10, 20, for example of 1.7 mm, facing one another andforming a space between them containing a layer of liquid crystals 5with a thickness of 15 μm. The internal surfaces 11′, 21′ have planaritydefects, and the thickness of the liquid crystals is variable.

In the “off” state (translucent state), the light transmission closelyrelated to the thickness of the layer of liquid crystals is thereforenot uniform. The quality of the product is therefore unacceptable,because of the visually observable dark and light regions.

In order to ensure good optical uniformity, the coated glass panesshould therefore have limited dioptric defects.

The glass panes according to the invention ensure a sufficiently uniformthickness of the layer of liquid crystals over the entire surface, andtherefore little variation in its optical performance. This avoids aglazing reject rate and therefore improves its reliability.

We will define a dioptric defect and a measurement method below.

We can define the profile of the internal face of each glass sheet(coated or not) in question by y(x), where x denotes the position on theinternal face. The variation of this profile can be characterized by theoptical reflection power ORP, which is defined by the followingrelationship:

${O\; R\; P_{(x)}} = {{2\frac{\mathbb{d}^{2}y_{(x)}}{\mathbb{d}x^{2}}} = {2y_{(x)}^{''}}}$

The variation of y(x) is due to the two phenomena:

-   -   undulations of the sheet of glass,    -   thickness defects (non-parallelism of the 2 faces of the glass        sheet).

This quantity is expressed in dioptres (m⁻¹) for y(x) expressed inmeters.

If the second derivative y″(x) is zero, this means that the internalface of the glass is perfectly flat; if the second derivative is lessthan 0, this means that the internal face of the glass is concave; andif the second derivative is greater than 0, this signifies that theinternal face of the glass is convex.

The method for measuring the planarity y(x) of the internal face of theglass is a contactless optical measurement method, which consists inanalysing the contrast at every point of a so-called umbrascopic imageobtained by reflection of a homogeneous light source from the internalsurface of the glass.

The unmeasured external face of the glass sheet is wetted with a liquidhaving an index similar to that of the glass, in order to eliminate anyreflection of the light from this surface and keep only the image of thedirectly illuminated internal face.

The planarity is thus measured every millimeter over the illuminatedsurface of the internal face. Each point is quantified by a physicalunit of optical power in millidioptres (mdt=dioptre/1000), similar toconverging and diverging lenses.

The final planarity is quantified by a dioptric defect score, whichcorresponds to the standard deviation of all the measurements. Thisscore, expressed in millidioptres (mdt), perfectly characterizes theplanarity of the measured surface. The score increases when theplanarity is degraded. For a given dioptric defect score, the amplitudeof the variation of y(x) also depends on the periodicity or pitch.

By way of example, for a sinusoidal profile y(x) with a pitch of 30 mm,a dioptric defect of 10 mdt corresponds to a profile variation of about+/−0.20 μm. In the worst case, the spatial variation of an assembly oftwo glass sheets (and therefore the thickness variation E of the liquidcrystals) is then doubled, i.e. about +/−0.40 μm. For a defect with apitch of 15 mm, the same 10 mdt dioptric defect corresponds to a profilevariation of +/−0.05 μm, and the thickness variation E of the liquidcrystals is therefore +/−0.10 μm in the worst case.

The pitch of dioptric defects of a sheet of float glass covers a rangefrom a few millimeters to a few tens of millimeters. Being closelylinked with the uniformity of the thickness E of the liquid crystals,the uniformity of light transmission in the “off” state results from allthe dioptric defects with all the pitches.

The uniformity of light transmission in the “off” state is alsoconditioned by the average thickness E of LC. The greater the thicknessE is, the more a thickness variation can be tolerated. This is why,according to the invention, a score is established as a function of theaverage thickness.

The dioptric defects of float glass are principally linked with the rateof advance of the glass (drawing rate of the line). The greater theglass advance rate is, the greater the dioptric defects are. For a givencapacity (or tonnage, daily) and a given raw width of glass, the glassadvance rate is inversely proportional to the thickness A of the glasssheet. Therefore, the thinner the glass sheet is, the higher the glassadvance rate is and the greater the dioptric defects are.

Thus, it is not possible to use an arbitrary thickness because it is thedioptric quality of the glass which determines the possible thickness ofthe glass. The invention allows us to select glass panes thinner than 6mm while guaranteeing the quality of the final product. The inventionallows us, for example, to use the smallest possible thickness whileguaranteeing the optical quality of the final product. For example, 2 mmglass panes may be selected so long as these glass panes are producedwith a drawing rate which is low enough to ensure limitation of dioptricdefects.

Furthermore, even with a 6 mm glass pane if the tonnage is too high, forexample 2000 tonnes/day, the dioptric defects will be too great.

The electrode in layer(s) has no significant influence on the dioptricdefects. Thus, if a “bare” float glass is suitable, the glass coatedwith an electrode layer will also be suitable.

Naturally, for the sake of simplicity and economy, it is preferable toselect suitable float glasses rather than to have to smooth (polishingetc.) any glass obtained by another manufacturing method.

The invention furthermore makes it possible to produce high-performanceliquid-crystal multiple glazings with a width of more than 1 m.

In a preferred embodiment,

-   -   for a thickness E of less than 30 μm, the thickness A of the        first glass sheet and the second glass sheet lies between 3 mm        and 5.5 mm inclusive of these values, in particular by        production on a float line with a capacity of at least 550        tonnes/day and preferably limited to 700 tonnes/day or    -   for a thickness E greater than or equal to 30 μm, the thickness        A of the first glass sheet and the second glass sheet lies        between 2 mm and 5.5 mm inclusive of these values, in particular        by production on a float line with a capacity of at least 550        tonnes/day and preferably limited to 700 tonnes/day.

Furthermore, the sealing joint has a given width L and may preferably beinterrupted in its width by a plurality of openings each defininglateral joint ends, and for each opening an additional sealing materialforms a bridge between the lateral ends of the joint, in particularconsisting of the said sealing material, thus forming materialcontinuity.

In the multiple glazing with liquid crystals of the prior art, thesealing joint is continuous.

With openings—supplemented with additional sealing—according to theinvention interrupting the joint of such multiple glazing with liquidcrystals, the optical performance (in the off state) is improved bycontributing, particularly in the edge regions of the layer of liquidcrystals, to uniform distribution of the layer of liquid crystals.

The inventive use of such openings—supplemented with additionalsealing—constitutes an invention per se. In a preferred embodiment,however, it is coupled with glass panes as defined above having alimited thickness A and a limited dioptre score.

Furthermore, it is in fact possible to use all the liquid-crystalsystems known by the terms “NCAP” (Nematic Curvilinearly Aligned Phases)or “PDLC” (Polymer Dispersed Liquid Crystal) or “CLC” (CholestericLiquid Crystal) or “NPD-LCD” (Non-homogenous Polymer Dispersed LiquidCrystal Display).

These may furthermore contain dichroic colourants, particularly insolution in the droplets of liquid crystals. The scattering of light andthe absorption of light by the systems can then jointly be modulated.

It is also possible to use, for example, gels based on cholestericliquid crystals containing a small quantity of crosslinked polymer, suchas those described in Patent WO-92/19695. More broadly speaking, “PSCTs”(Polymer Stabilized Cholesteric Texture) may therefore be selected.

Naturally, the liquid-crystal system may extend substantially over theentire surface of the glazing (except for the margins) or over (atleast) one restricted region. The liquid-crystal system may bediscontinuous, in a plurality of pieces (for example of the pixel type).

Multiple glazing with variable scattering by liquid crystals, as definedabove, may be used as glazing in vehicles or buildings.

The glazing according to the invention may be used in particular:

-   -   as an internal partition (between two rooms or in an area) in a        building, in a means of land, air or aquatic locomotion (between        two compartments, in a taxi, etc.),    -   as a glazed door, a window, a ceiling, a tile (floor, ceiling),    -   as a rear-view mirror of a vehicle, side glazing, a roof of a        means of land, air or aquatic locomotion,    -   as a projection screen,    -   as a shop frontage, a window in particular of a shop counter.

Naturally, the glazing according to the invention may form all or partof a partition, other window structure (such as a fanlight etc.), ormultiple glazing (with the addition of extra glazing).

The invention also relates to a method for producing multiple glazingwith variable scattering by liquid crystals, as defined above,comprising the following steps:

-   -   formation of the sealing joint, comprising application of the        sealing material (preferably essentially organic, in particular        epoxy resin) on the first float glass sheet (at the border)        provided with the first electrode,    -   (before or after formation of the sealing joint) liquid        deposition of the layer of liquid crystals with an average        thickness E on the first float glass sheet provided with the        first electrode and optionally on the second float glass sheet        provided with the second electrode,    -   after formation of the sealing joint and deposition of the layer        of liquid crystals, bringing the first and second glass sheets        in contact, in particular by calendering or pressing,    -   and before bringing the first and second glass sheets in        contact, formation of the plurality of the said openings of the        sealing joint, each defining lateral joint ends, by        discontinuous application of the sealing material and/or by        continuous application of the sealing material and the creation        of interruptions forming the openings.

At least two openings are preferably positioned facing a first sheetedge (sheet with straight or curved edges) and at least two otheropenings facing a second edge opposite the first edge, these edgescorresponding to the edges of the direction of the calendering, in thecase of calendering.

In the case of pressing in particular, at least two openings are alsopositioned facing a third edge adjacent to the first edge (and to thesecond edge) and at least two other openings facing a fourth edgeopposite the third edge.

The method may furthermore comprise application of the additionalsealing material, forming a bridge between the lateral ends of thejoint.

The additional sealing material may consist of the said sealingmaterial, thus forming material continuity, preferably essentiallyorganic, in particular epoxy resin.

Preferably, the width between the lateral ends of the joint may be atleast 5 mm, for example 10 mm.

Other details and features of the invention will become apparent fromthe following detailed description, which is provided with reference tothe appended drawings in which:

FIG. 1 (already described) represents a schematic sectional view ofreference multiple glazing with variable scattering by liquid crystals,not according to the invention,

FIG. 2 represents a schematic sectional view of multiple glazing withvariable scattering by liquid crystals in a first embodiment accordingto the invention,

FIG. 3 shows the layout diagram of the measurement of the dioptricdefect score,

FIG. 4 shows the principle of the formation of an umbrascopic image on ascreen on the basis of a planarity profile Y(x) of the glass,

FIG. 5 shows an example of a local illumination profile E(x) and anaverage illumination profile E0(x),

FIG. 6 represents a schematic view from below of multiple glazing withvariable scattering by liquid crystals according to the invention,showing in particular the sealing joint and the openings,

FIG. 6bis represents a schematic plan view of the multiple glazing withvariable scattering by liquid crystals, showing in particular thesealing joint and the openings, in a variant of FIG. 6,

FIG. 7 represents a schematic plan view of the manufacture of themultiple glazing with variable scattering by liquid crystals accordingto the invention, showing in particular the sealing joint and theopenings.

The exemplary embodiment represented in FIG. 2 shows the design of theliquid-crystal multiple glazing according to the invention in a firstembodiment.

On two sheets of float glass 1 and 1′, electrically conductive layers 3,4 with a thickness of about 20 to 400 nm, having external surfaces 21,31 and made for example of indium tin oxide (ITO), are arranged on theinternal faces 11, 21. The ITO layers have an electrical sheetresistance of between 5 Ω/□ and 300 Ω/□. Instead of layers made of ITO,other layers of electrically conductive oxide or layers of silver whosesheet resistance is comparable may also be used for the same purpose.

The layer 5 of liquid crystals, which may have a thickness of about 15to 60 μm, is placed between the electrode layers 3 and 4.

The layer 5 of liquid crystals contains spherical spacers. The spacers 6consist of a transparent hard polymer. For example, the product fromSekisui Chemical Co., Ltd, known by the designation “Micropearl SP” hasproven highly suitable as a spacer.

In order to ensure uniformity of the thickness E of the liquid-crystallayer 5 and thus ensure the optical performance of the glazing withliquid crystals, glass panes 1, 1′ with their electrodes 3, 4 are eachselected with a dioptric defect score according to the invention, whichscore is measured by umbrascopy in reflection.

The basic principle is associated with the geometrical optics. Thediagram of the layout is represented in FIG. 3.

From a very thin source, such as a projector 100, a light flux isprojected onto the face of the glass sheet 11 (coated or not with theelectrode) intended to be the internal face. A projected image isobserved on a screen 300 after reflection from the internal face 11 ofthe glass sheet. This image is acquired by a digital camera 200 in orderto be processed. The reflection from the second face 12 is neutralizedby using a wetted black fabric which is placed behind the glass pane 1and on which the glass is bonded by capillary effect.

FIG. 4 indicates the principle of the formation of an umbrascopic imageon the screen 300 on the basis of a planarity profile Y(x) of the glass.A concave region on the glass pane (convergent defect) causesconcentration of the incident reflected light 110 and therefore localover-illumination on the screen 300. A complex region on the glass(divergent defect) causes spreading of the incident reflected light 120and therefore local under-illumination on the screen 300.

FIG. 5 shows an example of a local illumination profile E(x) and anaverage illumination profile E0(x).

When the local illumination E(x) is equal to the average illuminationE0(x), the contrast is zero and consequently Y″(x)=0 and the opticalpower is zero.

When the local illumination E(x) is greater than the averageillumination E0(x), the contrast is negative and Y″(x)<0. A convergentdefect is therefore involved, which corresponds to a concavity on theglass pane.

When the local illumination E(x) is less than the average illuminationE0(x), the contrast is positive and Y″(x)>0. A divergent defect istherefore involved, which corresponds to a convexity on the glass pane.

Knowing that the planarity variations are more significant in thedirection of the overall width, in order to explain the operatingprinciple of the apparatus we will consider a planarity profile in theplane perpendicular to the casting direction and perpendicular to thesurface of the glass. It can be shown on the basis of the laws ofgeometrical optics and conservation of energy that there is arelationship between the illumination E(x) measured on the screencorresponding to an abscissa point x on the glass pane and the profileY(x) of the surface of the glass pane.

Certain geometrical simplifications made on the basis of the followingaspects: the layout is in quasi-normal reflection and the source isconsidered to be a point source, give the following relationship:

$\frac{\mathbb{d}^{2}{Y(x)}}{\mathbb{d}x^{2}} = {\frac{1}{D}\left( {\frac{E_{0}}{E(x)} - 1} \right)}$with:

-   Y(x): profile of the glass pane-   D: the glass pane—screen distance-   E₀: average illumination at x (that which would be obtained without    a planarity defect)

Let the optical reflection power ORP (in dioptres) be:

${O\; R\; P} = {{2 \times \frac{\mathbb{d}^{2}{Y(x)}}{\mathbb{d}x^{2}}} \approx {2 \times \frac{C(x)}{D}}}$with the contrast C(x) such that

${C(x)} = {\frac{E_{0} - {E(x)}}{E(x)}.}$

The contrast corresponds to the visual perception of the “linearity”(here in dashes because a profile rather than a surface is beingconsidered) observed on the umbrascopic image projected onto the screen.

Processing software calculates the contrast, and therefore the opticalreflection power ORP, for each pixel of the image.

The dioptric defect score (in millidioptres) reflects the homogeneity ofthe optical powers and is in fact the standard deviation σ of thedistribution of the optical reflection powers over the internal face,defined by the relationship:

$\sigma = \sqrt{\overset{\_}{\left( {O.P.r^{2}} \right)_{i,j}} - {\overset{\_}{\left( {O.P.r} \right)}}_{i,j}^{2}}$with

(O,P,r²)_(i,j) : mean square of the optical powers over the entireinternal face

(O,P,r)_(i,j) ² : square of the mean of the optical powers over theentire internal face.

The score must be less than 12 E/15 in order to ensure a sufficientoptical quality in transmission, that is to say a good homogeneity ofthe light transmission in the “off” state.

By way of example, for a thickness E of 15 μm with a standard float linehaving a capacity of 600 tonnes/day with a raw glass width of 3.5 m:

-   -   the score of the 2.1 mm glass is less than 22 mdt,    -   the score of the 3 mm glass is less than 11 mdt,    -   the score of the 4 mm glass is less than 8 mdt.

Furthermore, it is also possible to use known compounds for the layer ofliquid crystals, for example the compounds described in Document U.S.Pat. No. 5,691,795. The liquid-crystal compound from Merck Co., Ltd,marketed under the brand name “Cyanobiphenyl Nematic Liquid Crystal E-31LV” has also proven particularly suitable. In the case of thisembodiment, this product is mixed in a ratio of 10:2 with a chiralsubstance, for example 4-cyano-4′-(2-methyl)butylbiphenyl, and thismixture is mixed in a ratio of 10:0.3 with a monomer, for example4,4′-bisacryloylbiphenyl, and with a UV initiator, for example benzoinmethyl ether. The mixture prepared in this way is applied onto one ofthe coated glass sheets. After curing of the layer of liquid crystals byirradiation with a UV light, a polymer network is formed in which theliquid crystals are incorporated.

As a variant, the layer of liquid crystals does not contain astabilizing polymer but consists only of the compound comprising liquidcrystals and spacers. The compound comprising liquid crystals istherefore applied as such without a monomer additive, with a thicknessof from 3 to 20 μm onto one of the glass sheets 1, 1′. Compounds forliquid-crystal layers of this type are described, for example, inDocument U.S. Pat. No. 3,963,324.

For the layer of liquid crystals, it is possible to use PDLCs such asthe compounds 4-((4-ethyl-2,6-difluorophenyl)-ethinyl)-4′-propylbiphenyl and 2-fluoro-4, 4′-bis(trans-4-propylcyclohexyl)-biphenyl, for example marketed by the companyMerck under the reference MDA-00-3506.

On the edge, the layer of liquid crystals is sealed by an adhesivesealing joint 5 which simultaneously serves to firmly and permanentlybond the glass sheets 1, 1′.

The adhesive sealing material which seals the separate glass sheets 1and 1′ on their edges contains an epoxy resin.

As shown in FIG. 6, the sealing joint has a given width L and isinterrupted in its width by a plurality of openings 81 to 84, eachdefining lateral joint ends 71 to 74′.

More precisely, the sealing joint 7 is interrupted in its width by twoopenings 81 to 82 facing a first edge of the glazing and by two otheropenings 83, 84 facing a second edge opposite to the first edge, theseedges corresponding to the edges of the assembly direction of the glasspanes, preferably by calendering.

For each opening, an additional sealing material 7′ forms a bridgebetween the adjacent lateral ends of the joint, in particular consistingof the said sealing material, thus forming material continuity as shownin FIG. 6bis.

In the initial state (“off” state), that is to say before theapplication of an electrical voltage, this liquid-crystal glazing 100 istranslucent, that is to say it optically transmits but is nottransparent. As soon as the current is connected up, the layer of liquidcrystals changes under the effect of the alternating electric field intothe transparent state, that is to say the state in which viewing is nolonger prevented.

The electrically controllable glazing with liquid crystals is producedby using a method described in detail below.

In an industrial installation for continuous coating, by using themethod of magnetic field enhanced reactive sputtering, float glasssheets according to the invention are coated in successive sputteringchambers with a layer of ITO having an approximate thickness of 100 nm.

Two separate glass sheets of the same size and having the desireddimensions are cut from a large sheet of glass coated in this way andare prepared for continuation of the processing.

The two separate glass sheets cut to the desired dimensions then firstlyundergo a washing operation.

The liquid-crystal layer mixed with the spacers is then applied onto oneof the two glass sheets processed in this way. Since the two separateglass sheets are subsequently connected permanently and closely to oneanother on their edges by a sealing joint, the edge part of the glasssheet 1 is not coated over a width of about 2 to 10 mm.

The coating with the liquid-crystal compound is carried out with the aidof an operation referred to as drop-by-drop filling. In order to carryout the operation, a drop-by-drop pouring apparatus is used which makesit possible to deposit drops of liquid crystals onto a glass substrate,the quantity poured being finely adjustable.

In another embodiment of the method, in order to print the layer ofliquid crystals, a screen printing fabric is used with a mesh the widthof which is about 20 to 50 μm and the thread diameter of which is about30 to 50 μm.

The adhesive layer forming the joint 7 is likewise applied directlyalong the edge of the glass sheet 24 before or after deposition of thelayer of liquid crystals. It may have a width of, for example, from 2 to10 mm.

As shown by FIG. 7, the formation of a plurality of openings 81 to 84 inthe sealing joint is provided, with a size and distribution adapted toremove the excess liquid-crystal layer, the openings 81 to 84 eachdefining two adjacent lateral ends 71 to 74′ of the joint 7.

Furthermore, in order to do this, the application of the sealingmaterial is either discontinuous or is continuous then followed bycreation of openings (by removing material 7).

This is followed by application of the additional sealing material 7′forming a bridge between the lateral ends of the joint 71 to 74′,preferably consisting of the said sealing material, thus forming sealingmaterial continuity.

When the two separate glass sheets have thus been pressed against oneanother, the adhesive layer 7 is compressed to the thickness E of thelayer of liquid crystals.

The openings 81 to 84 therefore serve:

-   -   to remove the excess liquid-crystal layer, and therefore to        better control the layer thickness and thus avoid a loss of        optical quality,    -   to degas the layer of liquid crystals in order to avoid the        subsequent formation of bubbles in the layer and thus again to        avoid a loss of optical quality.

At least two openings are preferably positioned on the front edge of thecalendering and at least two openings on the rear edge of thecalendering.

The width of the lateral ends is, for example, 10 mm. The more viscousthe layer of liquid crystals is, the greater is the number of openingsused.

The calendering operation is subsequently carried out, or as a variantthe pressing.

If the layer of liquid crystals consists of a mixture of liquid crystalsand a monomer, the polymerization operation is then carried out byirradiation with UV light.

The invention claimed is:
 1. A multiple glazing with variable scatteringby liquid crystals comprising: first and second glass sheets sealed onan edge of their internal faces by a sealing joint; on the internalfaces of the first and second glass sheets, first and second electrodesin the form of transparent electrically conductive layers provided witha power supply; and on the first and second electrodes, a layer ofliquid crystals adapted to alternate reversibly between a transparentstate and a translucent state by application of an alternating electricfield, wherein a thickness of each of the first and second glass sheetsis less than or equal to 5.5 mm, and wherein each of the internal facescoated with the first and second electrodes has a dioptric defect score,expressed in millidioptres, of less than 12E/15 where the thickness E ofthe liquid crystals is in μm.
 2. The multiple glazing with variablescattering by liquid crystals according to claim 1, wherein for athickness E of less than 30 μm, the thickness of the first glass sheetand the second glass sheet lies from 3 mm to 5.5 mm, and for a thicknessE greater than or equal to 30 μm, the thickness of the first glass sheetand the second glass sheet lies from 2 mm to 5.5 mm.
 3. The multipleglazing with variable scattering by liquid crystals according to claim1, wherein the sealing joint has a width and is interrupted in its widthby a plurality of openings each defining lateral joint ends, and whereinfor each opening an additional sealing material forms a bridge betweenthe lateral ends of the joint, thus forming material continuity.
 4. Themultiple glazing with variable scattering by liquid crystals accordingto claim 3, wherein the sealing joint is interrupted in its width by atleast two openings facing a first edge of the glazing and by at leasttwo other openings facing a second edge opposite the first edge.
 5. Themultiple glazing with variable scattering by liquid crystals accordingto claim 1, wherein the sealing joint and/or an additional sealingmaterial is essentially organic.
 6. The multiple glazing with variablescattering by liquid crystals according to claim 5, wherein the sealingjoint and/or the additional sealing material is made of epoxy resin. 7.A method comprising arranging the multiple glazing with variablescattering by liquid crystals according to claim 1 as glazing invehicles or buildings.
 8. A method for producing multiple glazing withvariable scattering by liquid crystals according to claim 1, comprising:forming the sealing joint, said forming comprising applying the sealingmaterial on the first glass sheet provided with the first electrode;liquid depositing the layer of liquid crystals with an average thicknessE on the first glass sheet provided with the first electrode andoptionally on the second glass sheet provided with the second electrode;after forming the sealing joint and depositing the layer of liquidcrystals, bringing the first and second glass sheets in contact; andbefore bringing the first and second glass sheets in contact, formingthe plurality of said openings of the sealing joint each defining thelateral ends of the joint.
 9. The method for producing multiple glazingwith variable scattering by liquid crystals according to claim 8,wherein the sealing joint is interrupted in its width by at least twoopenings facing a first edge of the glazing and by at least two otheropenings facing a second edge opposite the first edge, and wherein theassembly of the first and second glass sheets is carried out bycalendering, the first and second edges corresponding to the edges inthe direction of calendering.
 10. The method for producing multipleglazing with variable scattering by liquid crystals according to claim9, wherein the assembly of the first and second glass sheets is carriedout by pressing, wherein the sealing joint is interrupted in its widthby at least two openings facing a third edge of the glazing adjacent tothe first edge and by at least two other openings facing a fourth edgeopposite the third edge.
 11. The method for producing multiple glazingwith variable scattering by liquid crystals according to claim 8,comprising applying the additional sealing material, forming a bridgebetween the lateral ends of the joint.
 12. The method for producingmultiple glazing with variable scattering by liquid crystals accordingto claim 11, wherein the additional sealing material consists of saidsealing material, thus forming material continuity.
 13. The method forproducing multiple glazing with variable scattering by liquid crystalsaccording to claim 12, wherein the additional sealing material is madeof epoxy resin.
 14. A multiple glazing comprising: first and secondglass sheets each having a face sealed on an edge thereof by a sealingjoint; first and second electrodes arranged respectively on the face ofthe first and second glass sheets, each of the first and secondelectrodes including an electrically conductive layer provided with apower supply; a layer of liquid crystals arranged on the first andsecond electrodes and adapted to alternate reversibly between atransparent state and a translucent state when an alternating electricfield is applied, wherein a thickness of each of the first and secondglass sheets is less than or equal to 5.5 mm, and wherein each of thefaces coated, respectively, with the first and second electrodes has adioptric defect score, expressed in millidioptres, of less than 12E/15where the thickness E of the liquid crystals is in μm.